Polycystic kidney disease (PKD) is a genetic disorder
characterized by the growth of numerous cysts in the kidneys. The
kidneys are two organs, each about the size of a fist, located in
the upper part of a person's abdomen, toward the back.

The kidneys filter wastes and extra fluid from the blood to form
urine. They also regulate amounts of certain vital substances in
the body. When cysts form in the kidneys, they are filled with
fluid. PKD cysts can profoundly enlarge the kidneys while replacing
much of the normal structure, resulting in reduced kidney function
and leading to kidney failure.

When PKD causes kidneys to fail-which usually happens after many
years-the patient requires dialysis or kidney transplantation.
About one-half of people with the most common type of PKD progress
to kidney failure, also called end-stage renal disease (ESRD).

PKD can also cause cysts in the liver and problems in other
organs, such as blood vessels in the brain and heart. The number of
cysts as well as the complications they cause help doctors
distinguish PKD from the usually harmless "simple" cysts that often
form in the kidneys in later years of life.

Types of
PKD

In the United States, about 600,000 people have PKD, and cystic
disease is the fourth leading cause of kidney failure. Two major
inherited forms of PKD exist:

Autosomal dominant PKD is the most common
inherited form. Symptoms usually develop between the ages of 30 and
40, but they can begin earlier, even in childhood. About 90 percent
of all PKD cases are autosomal dominant PKD.

Autosomal recessive PKD is a rare inherited
form. Symptoms of autosomal recessive PKD begin in the earliest
months of life, even in the womb.

Autosomal Dominant
PKD

Autosomal dominant PKD is the most common inherited disorder of
the kidneys. The phrase "autosomal dominant" means that if one
parent has the disease, there is a 50 percent chance that the
disease gene will pass to a child. In some cases-perhaps 10
percent-autosomal dominant PKD occurs spontaneously in patients. In
these cases, neither of the parents carries a copy of the disease
gene.

Many people with autosomal dominant PKD live for
several decades without developing symptoms. For this reason,
autosomal dominant PKD is often called "adult polycystic kidney
disease." Yet, in some cases, cysts may form earlier in life and
grow quickly, causing symptoms in childhood.

The cysts grow out of nephrons, the tiny filtering units inside
the kidneys. The cysts eventually separate from the nephrons and
continue to enlarge. The kidneys enlarge along with the cysts-which
can number in the thousands-while roughly retaining their kidney
shape. In fully developed autosomal dominant PKD, a cyst-filled
kidney can weigh as much as 20 to 30 pounds. High blood pressure is
common and develops in most patients by age 20 or 30.

What are the symptoms of autosomal dominant PKD?

The most common symptoms are pain in the back and the
sides-between the ribs and hips-and headaches. The pain can be
temporary or persistent, mild or severe.

People with autosomal dominant PKD also can experience the
following complications:

urinary tract infections-specifically, in the kidney cysts

hematuria-blood in the urine

liver and pancreatic cysts

abnormal heart valves

high blood pressure

kidney stones

aneurysms-bulges in the walls of blood vessels-in the
brain

diverticulosis-small pouches bulge outward through the
colon

How is autosomal dominant PKD diagnosed?

Autosomal dominant PKD is usually diagnosed by kidney imaging
studies. The most common form of diagnostic kidney imaging is
ultrasound, but more precise studies, such as computerized
tomography (CT) scans or magnetic resonance imaging (MRI) are also
widely used. In autosomal dominant PKD, the onset of kidney damage
and how quickly the disease progresses can vary. Kidney imaging
findings can also vary considerably, depending on a patient's age.
Younger patients usually have both fewer and smaller cysts.

Doctors have therefore developed specific criteria for
diagnosing the disease with kidney imaging findings, depending on
patient age. For example, the presence of at least two cysts in
each kidney by age 30 in a patient with a family history of the
disease can confirm the diagnosis of autosomal dominant PKD. If
there is any question about the diagnosis, a family history of
autosomal dominant PKD and cysts found in other organs make the
diagnosis more likely.

In most cases of autosomal dominant PKD, patients have no
symptoms and their physical condition appears normal for many
years, so the disease can go unnoticed. Physical checkups and blood
and urine tests may not lead to early diagnosis. Because of the
slow, undetected progression of cyst growth, some people live for
many years without knowing they have autosomal dominant PKD.

Once cysts have grown to about one-half inch, however, diagnosis
is possible with imaging technology. Ultrasound, which passes sound
waves through the body to create a picture of the kidneys, is used
most often. Ultrasound imaging does not use any injected dyes or
radiation and is safe for all patients, including pregnant women.
It can also detect cysts in the kidneys of a fetus, but large cyst
growth this early in life is uncommon in autosomal dominant
PKD.

More powerful and expensive imaging procedures such as CT scans
and MRI also can detect cysts. Recently, MRI has been used to
measure kidney and cyst volume and monitor kidney and cyst growth,
which may serve as a way to track progression of the disease.

Diagnosis can also be made with a genetic test that detects
mutations in the autosomal dominant PKD genes, called PKD1
and PKD2. Although this test can detect the presence of
the autosomal dominant PKD mutations before large cysts develop,
its usefulness is limited by two factors: detection of a disease
gene cannot predict the onset of symptoms or ultimate severity of
the disease, and if a disease gene is detected, no specific
prevention or cure for the disease exists. However, a young person
who knows of a PKD gene mutation may be able to forestall the loss
of kidney function through diet and blood pressure control.

The genetic test may also be used to determine whether a young
member of a PKD family can safely donate a kidney to a family
member with the disease. Individuals with a family history of PKD
who are of childbearing age might also want to know whether they
have the potential of passing a PKD gene to a child. Anyone
considering genetic testing should receive counseling to understand
all the implications of the test.

How is autosomal dominant PKD treated?

Although a cure for autosomal dominant PKD is not available,
treatment can ease symptoms and prolong life.

Pain. Pain in the area of the kidneys can be
caused by cyst infection, bleeding into cysts, kidney stone, or
stretching of the fibrous tissue around the kidney with cyst
growth. A doctor will first evaluate which of these causes are
contributing to the pain to guide treatment. If it is determined to
be chronic pain due to cyst expansion, the doctor may initially
suggest over-the-counter pain medications, such as aspirin or
acetaminophen (Tylenol). Consult your doctor before taking any
over-the-counter medication because some may be harmful to the
kidneys. For most but not all cases of severe pain due to cyst
expansion, surgery to shrink cysts can relieve pain in the back and
sides. However, surgery provides only temporary relief and does not
slow the disease's progression toward kidney failure.

Headaches that are severe or that seem to feel different from
other headaches might be caused by aneurysms-blood vessels that
balloon out in spots-in the brain. These aneurysms could rupture,
which can have severe consequences. Headaches also can be caused by
high blood pressure. People with autosomal dominant PKD should see
a doctor if they have severe or recurring headaches-even before
considering over-the-counter pain medications.

Urinary tract infections. People with autosomal
dominant PKD tend to have frequent urinary tract infections, which
can be treated with antibiotics. People with the disease should
seek treatment for urinary tract infections immediately because
infection can spread from the urinary tract to the cysts in the
kidneys. Cyst infections are difficult to treat because many
antibiotics do not penetrate the cysts.

High blood pressure. Keeping blood pressure
under control can slow the effects of autosomal dominant PKD.
Lifestyle changes and various medications can lower high blood
pressure. Patients should ask their doctors about such treatments.
Sometimes proper diet and exercise are enough to keep blood
pressure controlled.

End-stage renal disease. After many years, PKD
can cause the kidneys to fail. Because kidneys are essential for
life, people with ESRD must seek one of two options for replacing
kidney functions: dialysis or transplantation. In hemodialysis,
blood is circulated into an external filter, where it is cleaned
before re-entering the body; in peritoneal dialysis, a fluid is
introduced into the abdomen, where it absorbs wastes and is then
removed. Transplantation of healthy kidneys into ESRD patients has
become a common and successful procedure. Healthy-non-PKD-kidneys
transplanted into PKD patients do not develop cysts.

Autosomal Recessive
PKD

Autosomal recessive PKD is caused by a mutation in the autosomal
recessive PKD gene, called PKHD1. Other genes for the
disease might exist but have not yet been discovered by scientists.
We all carry two copies of every gene. Parents who do not have PKD
can have a child with the disease if both parents carry one copy of
the abnormal gene and both pass that gene copy to their baby. The
chance of the child having autosomal recessive PKD when both
parents carry the abnormal gene is 25 percent. If only one parent
carries the abnormal gene, the baby cannot get autosomal recessive
PKD but could ultimately pass the abnormal gene to his or her
children.

The signs of autosomal recessive PKD frequently begin before
birth, so it is often called "infantile PKD." Children born with
autosomal recessive PKD often, but not always, develop kidney
failure before reaching adulthood. Severity of the disease varies.
Babies with the worst cases die hours or days after birth due to
respiratory difficulties or respiratory failure.

Some people with autosomal recessive PKD do not develop symptoms
until later in childhood or even adulthood. Liver scarring occurs
in all patients with autosomal recessive PKD and tends to become
more of a medical concern with increasing age.

What are the symptoms of autosomal recessive PKD?

Children with autosomal recessive PKD experience high blood
pressure, urinary tract infections, and frequent urination. The
disease usually affects the liver and spleen, resulting in low
blood cell counts, varicose veins, and hemorrhoids. Because kidney
function is crucial for early physical development, children with
autosomal recessive PKD and decreased kidney function are usually
smaller than average size. Recent studies suggest that growth
problems may be a primary feature of autosomal recessive PKD.

How is autosomal recessive PKD diagnosed?

Ultrasound imaging of the fetus or newborn reveals enlarged
kidneys with an abnormal appearance, but large cysts such as those
in autosomal dominant PKD are rarely seen. Because autosomal
recessive PKD tends to scar the liver, ultrasound imaging of the
liver also aids in diagnosis.

How is autosomal recessive PKD treated?

Medicines can control high blood pressure in autosomal recessive
PKD, and antibiotics can control urinary tract infections. Eating
increased amounts of nutritious food improves growth in children
with autosomal recessive PKD. In some cases, growth hormones are
used. In response to kidney failure, autosomal recessive PKD
patients must receive dialysis or transplantation. If serious liver
disease develops, some people can undergo combined liver and kidney
transplantation.

Genetic Diseases

Genes are segments of DNA, the long molecules that reside in
each of a person's cells. The genes, through complex processes,
build proteins for growth and maintenance of the body. At
conception, DNA-or genes-from both parents are passed to the
child.

A genetic disease occurs when one or both parents pass abnormal
genes to a child at conception. If receiving an abnormal gene from
just one parent is enough to produce a disease in the child, the
disease is said to have dominant inheritance. If receiving abnormal
genes from both parents is needed to produce disease in the child,
the disease is said to be recessive. A genetic disease can also
occur through a spontaneous mutation.

The chance of acquiring a dominant disease is higher than the
chance of acquiring a recessive disease. A child who receives only
one gene copy for a recessive disease at conception will not
develop the genetic disease-such as autosomal recessive PKD-but
could pass the gene to the following generation.

Note: The information above was reproduced or
derived from the following public domain
sources: The National Digestive Diseases Information
Clearinghouse (NDDIC) http://digestive.niddk.nih.gov/index.htm, the
National Institute of Diabetes and Digestive and Kidney Diseases
(NIDDK) Reference Collection, and MedlinePlus, a service of
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